• Paul Eggert's avatar
    lisp.h: Fix a problem with aliasing and vector headers. · eab3844f
    Paul Eggert authored
    GCC 4.6.0 optimizes based on type-based alias analysis.  For
    example, if b is of type struct buffer * and v of type struct
    Lisp_Vector *, then gcc -O2 was incorrectly assuming that &b->size
    != &v->size, and therefore "v->size = 1; b->size = 2; return
    v->size;" must therefore return 1.  This assumption is incorrect
    for Emacs, since it type-puns struct Lisp_Vector * with many other
    types.  To fix this problem, this patch adds a new type struct
    vector_header that documents the constraints on layout of vectors
    and pseudovectors, and helps optimizing compilers not get fooled
    by Emacs's type punning.  It also adds the macros XSETTYPED_PVECTYPE
    XSETTYPED_PSEUDOVECTOR, TYPED_PSEUDOVECTORP, for similar reasons.
    * lisp.h (XVECTOR_SIZE): New convenience macro.  All previous uses of
    XVECTOR (foo)->size replaced to use this macro, to avoid the hassle
    of writing XVECTOR (foo)->header.size.
    (XVECTOR_HEADER_SIZE): New macro, for use in XSETPSEUDOVECTOR.
    (XSETTYPED_PVECTYPE): New macro, specifying the name of the size
    member.
    (XSETPVECTYPE): Rewrite in terms of new macro.
    (XSETPVECTYPESIZE): New macro, specifying both type and size.
    This is a bit clearer, and further avoids the possibility of
    undesirable aliasing.
    (XSETTYPED_PSEUDOVECTOR): New macro, specifying the size.
    (XSETPSEUDOVECTOR): Rewrite in terms of XSETTYPED_PSEUDOVECTOR
    and XVECTOR_HEADER_SIZE.
    (XSETSUBR): Rewrite in terms of XSETTYPED_PSEUDOVECTOR and XSIZE,
    since Lisp_Subr is a special case (no "next" field).
    (ASIZE): Rewrite in terms of XVECTOR_SIZE.
    (struct vector_header): New type.
    (TYPED_PSEUDOVECTORP): New macro, also specifying the C type of the
    object, to help avoid aliasing.
    (PSEUDOVECTORP): Rewrite in terms of TYPED_PSEUDOVECTORP.
    (SUBRP): Likewise, since Lisp_Subr is a special case.
    * lisp.h (struct Lisp_Vector, struct Lisp_Char_Table):
    (struct Lisp_Sub_Char_Table, struct Lisp_Bool_Vector):
    (struct Lisp_Hash_Table): Combine first two members into a single
    struct vector_header member.  All uses of "size" and "next" members
    changed to be "header.size" and "header.next".
    * buffer.h (struct buffer): Likewise.
    * font.h (struct font_spec, struct font_entity, struct font): Likewise.
    * frame.h (struct frame): Likewise.
    * process.h (struct Lisp_Process): Likewise.
    * termhooks.h (struct terminal): Likewise.
    * window.c (struct save_window_data, struct saved_window): Likewise.
    * window.h (struct window): Likewise.
    * alloc.c (allocate_buffer, Fmake_bool_vector, allocate_pseudovector):
    Use XSETPVECTYPESIZE, not XSETPVECTYPE, to avoid aliasing problems.
    * buffer.c (init_buffer_once): Likewise.
    * lread.c (defsubr): Use XSETTYPED_PVECTYPE, since Lisp_Subr is a
    special case.
    * process.c (Fformat_network_address): Use local var for size,
    for brevity.
    eab3844f
xselect.c 84.1 KB